Boiling water nuclear reactors (BWR) have simple, robust designs and have been operating successfully in the US for many years. Based on this history of successful operation, many BWR operators want to extend the life of their reactors from the planned 35 years to 50 years and to increase the power from the reactors by about 15 to 20%. This increase in power may be obtained by simply increasing the rate of flow of steam, while keeping the total pressure in the system constant. This is possible because reactor power plants are designed to operate with the main control valves only 40% open. By opening the valves slightly more (to about 46-48% open) steam can be made to flow through the existing pipe system 15-20% faster, with no increase in the total pressure. As the power obtained from a steam turbine is proportional to the combination of steam density, which is directly proportional to pressure, and velocity, this will result in a corresponding increase in power output. Moreover, as there is no increase in total system pressure, the existing power station structure should not need to be changed in any fundamental way.
The only significant uncertainty in making such a change is in predicting the changes in flow-induced vibrations that will result from the increased flow rate of the steam. The existing plants have a long history of operating at the present flow rates and dealing with the resultant flow-induced vibrations. Changing the rate of flow is going to change the vibrations, but exactly how they will change is not easy to predict or to measure.
The lack of predictability occurs, in part, because most flow-induced vibration mechanisms involve shear layers, and therefore scale with dynamic pressure at a constant Mach number. (Dynamic pressure is the component of a fluid pressure that represents fluid kinetic pressure and is equal to one half the fluid density multiplied by the square of the fluid velocity). Because the BWR power increases are obtained at constant total pressure by increasing the velocity of the steam flow, both the Mach number, and the dynamic pressure, increase. Simple scaling laws are therefore, not so easily deduced. Moreover, a real BWR system has a multitude of geometric discontinuities, such as junctions and branch lines of various lengths and diameters, making the prediction of the flow-induced vibrations that will result from the increased steam flow an extremely complex task.
Direct measurement of the effects of the changed flow induced vibrations is prohibitively expensive, because fitting measurement devices to components within the steam dome is extremely expensive and, because the fitted devices do not last long in the high temperatures and highly radioactive conditions within the steam dome.
What is needed is an inexpensive and reliable system and method for estimating the fluctuating pressure loads on components within a BWR steam dome without the need to make measurements within the BWR steam dome.